The present invention generally relates to fuel burner apparatus and, in a preferred embodiment thereof, more particularly relates to a heating appliance having a specially designed flame spreader-type fuel burner with lowered NOx (i.e., oxides of nitrogen) emissions.
Fuel-fired heating appliances such as furnaces, boilers and water heaters typically utilize combustion heat from a burner structure to controllably add heat to a heated medium such as air or water as the case may be. As might be imagined, these burner structures come in a wide variety of types, constructions and designs--each having its design strengths and weaknesses. In one particular type of fuel burner, to which the present invention is directed, a burner member from which flames emanate is positioned beneath a device typically referred to as a "flame spreader".
The flame spreader is typically a solid sheet of metal or other suitable noncombustible material, has a circular flat disc shape or a downwardly concave "hubcap" shape, and has a peripheral edge portion which is horizontally outwardly spaced apart from the actual flame generating burner section of the overall burner apparatus. As the burner flames travel upwardly they impinge on the bottom side of the flame spreader and are horizontally deflected thereby until they reach the peripheral flame spreader edge and turn upwardly past such edge. The purpose of flame spreaders of this general type is to stabilize and shape their underlying burner flame. Illustrative of this type of burner/flame spreader apparatus is the burner structure depicted and described in U.S. Pat. No. 4,134,719 to Velie.
In flame spreader-types of fuel burners, in common with other types of fuel burners, an increasingly stringent design requirement is the reduction NOx emissions from the burner. It would thus be desirable to provide a fuel burner of the flame spreader type which had a lowered NOx emission level, and to obtain this goal without greatly increasing the cost of the overall burner assembly. It is accordingly an object of the present invention to provide such a lowered NOx emission flame spreader-type burner for use in a fuel-fired heating appliance.